1. Field of the Invention
The present invention relates to a detection device for detecting change in a magnetic field. More particularly, the invention relates to a moving object detection device suitably used when moving state of an object to be detected is magnetically detected. The object makes linear movement or rotary movement such as a rack or a gear made of soft magnetic substance in an industrial machine tool, or an engine of an automobile.
2. Description of the Prior Art
There is a method using a property that an output signal of a magnetic sensor element is changed in response to a soft magnetic body coming close to the magnetic sensor element applied magnetic field by a permanent magnet, in order to detect moving state of an object which makes a linear movement or rotary movement such as a rack or a gear of the soft magnetic body in an industrial machine tool or an engine of an automobile, etc.
A moving object detection device was proposed in Japanese Utility Model Application Laid-Open No. 4-21962, in which a housing is integrally formed by a resin, so that the housing can contain a magnetic sensor element to be a major element for detection of a moving state of an object to be detected, a permanent magnet for applying a magnetic field to the magnetic sensor element and terminals to which a protection (processing) circuit part receiving an output signal of the magnetic sensor element is connected for outputting a detected electric signal to the outside.
In such a moving object detection device, since the magnetic sensor element and protection (processing) circuit parts connected to the terminals by soldering are molded by integrally covering them with a resin, special consideration in designing is necessary to avoid any stress applied to the magnetic sensor element and the electronic parts, which are susceptible to stress. In addition, careful control in designing or manufacturing is necessary to avoid solder-connected spots being disconnected or shortened by heat and stress at the time of molding resin.
It may be also possible that the resin will be molded after attaching the magnetic sensor element and circuit parts for protecting (processing) the output signal on a board, however, some consideration is still required to avoid any occasion that the circuit parts are destroyed, and the soldered spots between the terminals and each circuit parts are disconnected or short when the board is warped or bent by the heat and stress at the time of molding resin.
Japanese Patent Application Laid-Open No. 2000-214176 discloses a device that overcomes those problems, for example. In the device, a magnetic sensor element, a permanent magnet for applying magnetic field to the magnetic sensor element, and a board implemented with a circuit for protecting (processing) an output signal of the magnetic sensor element are held by a holder and contained in a case made of resin. When an opening of the case is sealed with sealing resin, a passage hole for the sealing resin is provided on the board so as to prevent warping or bending of the board at the time of sealing with the sealing resin and hence, to prevent occurrence of disconnection or short circuit failure at a solder-connected spot and destruction of a circuit part.
The moving object detection device in accordance with the Japanese Patent Application Laid-Open No. 2000-214176 will be described according to a side sectional view in FIG. 10.
In FIG. 10, reference numeral 1 denotes a magnetic sensor element and reference numeral 2 for a permanent magnet for applying a required magnetic field to the magnetic sensor element, and the magnetic sensor element 1 and the permanent magnet 2 are held on a resin holder 3. A circuit part 6 for protecting (processing) an output signal of the magnetic sensor element 1 is implemented on a board 4, and the board 4 is also held on the holder 3. A resin passage hole 4a is formed substantially at the center of the board 4. When sealing resin is poured in a resin case 10 to seal an opening of the case, the sealing resin can pass through the hole 4a. Each end of conductors 5 is connected to the board 4. The conductors 5 are provided for leading an electric signal to the outside, which is made from an output signal detected by the magnetic sensor element 1 by a signal protection (processing) circuit on the board 4.
The resin case 10 is in the cylindrical shape with a bottom, and one end is an opening part 11 before sealed with the sealing resin, and a notch portion 12 is further formed from an edge of the opening part 11. A cover grommet 15 made of resin is fitted to the notch portion 12, and its inner surface 16 constitutes a mechanical fitting portion of a connector. A grommet 20 arranged inside the cover grommet 15 is an elastic body such as rubber, and the conductors 5 are inserted to each of through holes of the grommet 20.
Outer circumferential portions of the case 10 and the cover grommet 15 are covered with a molding body 25 of the sealing resin to form an attaching portion 26 and to seal the opening part 11 of the case 10.
In Japanese Patent Application Laid-Open No. 2000-214176, the device has such a structure that the magnetic sensor element, the permanent magnet and the board for the output signal protection (processing) circuit are held by the holder, the periphery is sealed by resin molding, the mounting portion to be mounted on an industrial machine tool or an automobile engine is formed and the connector portion for wiring/connection to an electric control system of the industrial machine tool or the automobile engine is formed. Accordingly, it has the following problems.
(1) When a quantity in one time production is small (i.e., small-lot production), preparation of die set for resin molding requires a number of processes, and improvement of production efficiency is limited.
(2) Since the sealing resin is poured and filled in the periphery of electronic parts implemented on a board for an output signal protection (processing) circuit, stress caused by expansion/contraction of the sealing resin is applied to the electronic parts and the connected spots due to change in atmospheric temperature in actual use. Thus, it is necessary to take measures for alleviating this stress in order to improve resistance to thermal shock.
(3) Since a waterproof structure is adopted by welding of the molded sealing resin to the resin case, it is necessary means for preventing separation of the welding interface of the sealing resin caused by change in atmospheric temperature in order to improve a life with respect to waterproof property.